A self-doping type electrically conducting polymer is usually soluble in water and easily shapable or film-formable into an arbitrary shape and by virtue of such properties, production of a large-area film is facilitated and such a polymer, for its excellent processability, can be employed in production of electrical elements requiring high-precision processing technology.
In recent years, by taking advantage of these properties, self-doping type electrically conducting polymers are used for prevention of charge-up in lithography process using a charged particle beam such as electron beam or ion beam.
A method of imparting water resistance to a water-soluble self-doping type electrically conducting polymer is disclosed. More specifically, a method of performing a dehydration treatment for enhancing the water resistance of a water-soluble polythiophene-based self-doping type electrically conducting polymer is disclosed (see, JP-A-3-221520 (the term “JP-A” as used herein means an “unexamined published Japanese patent application”)).
However, in this method, the water insolubility is attained by decreasing the amount of water contained, and the essential difference between the water-soluble self-doping type electrically conducting polymer and the water-insoluble self-doping type electrically conducting polymer is unclear since the document does not include description about it.
A method of heat-treating a substrate coated with a water-soluble aniline-based self-doping type electrically conducting polymer to obtain a water-resistant electric conductor is disclosed (see, JP-A-2001-98069).
However, in this method, the water resistance is imparted by eliminating a sulfonic acid group and/or a carboxyl group of the self-doping type electrically conducting polymer and therefore, the original electrical conductivity is disadvantageously liable to decrease. In particular, high temperature treatment, which causes decomposition of the self-doping type electrically conducting polymer itself, gives rise to a problem that the electrical conductivity is seriously decreased.
Also, a water-soluble polyisothianaphthene-based self-doping type electrically conducting polymer and a production process thereof are disclosed (see, JP-A-6-49183), but this aqueous solution is known to be affected by oxygen (see, JP-A-8-259673) and there is no known method for improving the water resistance and solvent resistance at present.
With respect to method for enhancing the water resistance and solvent resistance of an electrically conducting composition containing a self-doping type electrically conducting polymer, a method of adding a thermosetting matrix resin is disclosed in JP-A-2000-186218. In this method, a self-doping type electrically conducting polymer is used as a mixture with an insulating polymer and therefore the electrical conductivity decreases as compared with a case where a self-doping type electrically conducting polymer alone is used. Also, it is known that, in the case of using an electrically conducting composition as a coating film, since the coating film formed must have a large thickness so as to ensure predetermined electrical conductivity, transmission of the film thus formed is low as compared with a film formed of the self-doping type electrically conducting polymer alone.
Incidentally, an electronic device is used in the state that a self-doping type electrically conducting polymer-containing composition and various thin films are stacked. In this case, an electrically conducting polymer component of the electrically conducting polymer-containing composition or additives contained therein may dissolve out between the electrically conducting polymer composition layer and a thin film layer in contact therewith, or components of various thin film layers may dissolve out into the electrically conducting polymer composition layer, resulting in a problem that the performance of the electronic device seriously decreases. Thus, a material excellent in the solvent resistance as an electrically conducting composition is being demanded.
For example, the polymer-type organic light-emitting element developed to-date is typically constructed by providing anode (transparent)/anode buffer layer/light-emitting layer/cathode in this order on the transparent substrate and is used in the state that various thin films are stacked.
In this construction, the anode buffer layer is inserted for the purpose of flattening the anode surface to prevent an electrical short circuit or for the purpose of buffering the barrier against hole injection from the light-emitting layer into the anode. For this anode buffer, a mixture of poly(3,4-ethylenedioxythiophene) (PEDOT) which is an electrically conducting polymer material and polystyrenesulfonic acid (PSS) is being widely used at present.
Also, the present inventors have already proposed that a self-doping type electrically conducting polymer having an isothianaphthene skeleton showing weak acidity at 1% by mass is useful as the anode buffer layer.
In these techniques, the above-mentioned mixture of poly(3,4-ethylenedioxythiophene) (PEDOT) and polystyrenesulfonic acid (PSS) contains a sulfonic acid group in PSS working out to a dopant, and the self-doping type electrically conducting polymer also contains a sulfonic acid group in its molecular structure. Whichever of the electrically conducting polymers is used for the anode buffer layer, there remains another problem that water embraced as a crystal water in the sulfonic acid group is released in the device to deteriorate the element, which should be solved to avoid the deterioration.
Intensive studies are being made on such a problem regarding deterioration resulting from movement of water. In particular, a method of providing a barrier layer to prevent water present in ambient air which permeates into the element from reaching the light-emitting layer is disclosed (see JP-A-2004-134151).